Stimulation of respiratory mechanoreceptors during breathing and the central processing of afferent input play an important role in respiratory sensations, in the regulation of breathing, and the production of dyspnea. Respiratory sensation in normal subjects will be evaluated using the established psychophysical techniques of magnitude estimation and production, to determine the relationship between the physical dimensions of respiratory stimuli such as tidal volume, ventilation and resistive, elastic and threshold loads and the resulting subjective experience or psychological sensation. Studies will also be performed in patients with chronic obstructive lung disease and with pulmonary fibrosis to determine whether respiratory sensations in these patients differ from that in normals and whether alterations in respiratory sensation are related to the extent of intrinsic mechanical lung dysfunction and to the degree of dyspnea in these patients. The influence of respiratory sensation on efferent respiratory activity will be determined by comparing sensory magnitude with measures of respiratory muscle activity including EMG and muscle force and the magnitude of respiratory responses to chemical and mechanical stimuli. The mechanisms of respiratory sensation will be investigated by studies of patients with tracheostomies, and diaphragmatic and intercostal muscle paralysis in whom some of the receptors considered to mediate respiratory sensations have been destroyed or by-passed. The quantitative studies proposed will contribute to the understanding of the factors involved in the regulation of breathing in conscious man and provide further insights into the basis of dyspnea and the interplay of respiratory sensations and respiratory output in patients with lung disease.